Optical device for helmet visor comprising a Mangin mirror

ABSTRACT

An optical device for a system for the presentation of collimated images by a non-plane mirror, which makes it possible to present a user with an image corrected of distortion due to a non-plane mirror and exhibiting good resolution. To do this, the device includes a Mangin type mirror whose optical characteristics ensure good image quality of correction of off-centering distortion and good image sharpness. The Mangin type mirror has a reflecting surface and a layer of refracting material defining a refracting surface. One surface may be spherical, and the other aspherical. The surfaces may also be aspherical. One aspherical surface may be a paraboloid, an ellipsoid, or a torus. The refracting material can exhibit an optical index varying according to the position on the surface of the mirror. The device may be applied in particular to a system for the presentation of collimated images by a spherical mirror inclined with respect to the direction from which it is observed. The Mangin type mirror then corrects the off-centering distortion of the second kind due to this off-axis spherical mirror. The device may be applied in particular to helmet viewfinders for an aircraft pilot.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an optical device for the correction ofaberrations affecting an image. In particular, a device according to theinvention makes it possible to correct the distortion due to a sphericalconcave mirror that is inclined with respect to the direction at whichthis mirror is observed.

The invention can be applied especially but not exclusively to a helmetviewfinder for the pilot of a fighter aircraft or helicopter or for theoperator of a training simulator.

2. Discussion of the Background

A helmet viewfinder is an image-presenting device that is integratedinto a helmet. The viewfinder enables the wearer of the helmet, forexample the pilot of an aircraft in flight, to observe visualinformation simultaneously with the view of the landscape or of thepilot's cabin, which he perceives most usually through a protectivevisor.

The presentation of appropriate information, for example in the form ofsymbols, provides piloting and navigation assistance. Thus, for armedvehicles, the presentation of a reticule provides assistance in theaiming of a weapon.

The information may also consist of an image of the landscape acquiredby sensors other than the eye of the helmet wearer such as infraredimage sensors or light intensifiers to complement or replace directviewing.

Inside the helmet, an image generator comprises an imager whose screen,for example a cathode-ray tube screen or a liquid crystal screen,enables an image to be displayed.

The image is most usually conveyed by a relaying optic up to a combinerwhich presents the conveyed image in a state where it is superimposed onthe view of the landscape.

In order that the pilot may simultaneously observe the landscape vieweddirectly at infinity and the image from the imager, the latter image isalso focused at infinity by a collimation optic.

When the combiner is formed by a simple semi-reflective flat plate, thecollimation of the image can be achieved by an optic placed between theimager and the combiner. A prior art embodiment such as this has themajor drawback of requiring a collimation optic that requires far toomuch space in relation to the restricted field of view that is obtained.

To reduce the space requirement, a combiner with optical power has beenproposed. A combiner such as this provides its user with both thecollimation of the image and the superimposition of the collimated imagewith the view of the landscape.

The prior art has a very extensive variety of devices comprising acombiner with optical power. Of more particular interest areimage-presenting systems that comprise a spherical concave mirror tocollimate the image.

A concave spherical mirror achieves an average quality collimation of animage placed at a particular point in space located on the axis of themirror and at a distance from this mirror equal to half its radius ofcurvature. By placing an imager at this point, the eye located on theaxis of the mirror receives rays coming from the imager after they arereflected on the spherical mirror. These rays are parallel and lead tothe perception, by the eye, of a collimated image. If, furthermore, themirror is semi-reflective, it enables the same eye to observe thelandscape by transparency. However, in a device such as this, the imagerwould have to lie on the axis of the semi-transparent spherical mirrorand it would conceal the user's field of view.

To clear the user's view, the spherical mirror is inclined with respectto the normal to his/her face and the user's eye is no longer on theaxis of the mirror. This arrangement has the drawback of resulting in acollimated image that is affected by optical aberrations, especiallyoff-centring aberrations, which need to be corrected, at leastpartially.

The inclination of the spherical concave mirror afflicts the collimatedimage with distortion, known as off-centring distortion of the secondkind, characterized by a convergence of the verticals and an apparentcurvature of the horizontals.

In a patent filed under No. 97 09893 on Aug. 1, 1997 by the presentApplicant, an aspherical mirror with an adapted shape enables acorrection of the off-centring distortion of the second kind.

The particular surface of the proposed aspherical mirror enables amodification of the light rays in order to rectify the effects of thespherical concave mirror on the horizontals and verticals of the imageobserved and thus ensure a correction of the distortion. This correctionis achieved by the introduction through the aspherical mirror, of anoff-centring distortion of the second kind to compensate for thedistortion of the same type due to the spherical concave collimationmirror used off-axis. The aspherical mirror has the effect of making theverticals parallel and the horizontals rectilinear in the collimatedimage. The image is rectified and orthoscopic but the overall shape ofthe mirror causes a local amplification of the aberrations, andespecially of astigmatism. The correction of the distortion enabled bythis invention is limited by a deterioration of the resolution of theimage.

SUMMARY OF THE INVENTION

The problem is to construct a device for the presentation of imagescomprising an inclined non-plane collimation mirror presenting acollimated image that is satisfactory for the user, namely an image thatis devoid of troublesome aberrations and has a wide field of viewgreater than or equal to 40 degrees. This entails obtaining a collimatedimage that has both high resolution and high correction of thedistortion due to the inclination of the non-plane collimation mirror.For a spherical collimation mirror observed at an oblique angle withrespect to the axis of the mirror, this entails correcting anoff-centring distortion of the second kind. In this distortion, there isno symmetry of revolution.

This is why the invention proposes an optical device for a system forthe presentation of collimated images to a user, comprising an imager,an optical axis and a non-plane mirror inclined on the optical axis,characterized in that the optical device comprises optical means tocorrect the distortion of the image presented to the user, whichdistortion is due to the inclination of the non-plane mirror, the saidmeans comprising a Mangin mirror inclined on the optical axis.

The system for the presentation of images comprises an imager and acollimation mirror that sends a substantially collimated image, in theform of a beam of parallel light rays, back to the user. The inventionis most especially applicable to a spherical collimation mirror that isinclined with respect to the direction of the collimated rays.

The light rays coming from the centre of the imager form the centralfield of the imager. The optical axis of the device corresponds to thepath of the ray of the central field that goes through the centre of theuser's pupil.

The optical axis is most usually a jagged line. For example, if theimage is presented to the user straight ahead of him/her, the part ofthe optical axis located between the eye and the spherical mirror issupported by a first straight line normal to the centre of the user'spupil, the optical axis has a break at the intersection of this firststraight line with the inclined spherical mirror and the image that thespherical mirror gives of this first straight line supports thefollowing segment of the optical axis.

According to the invention, a Mangin type mirror is placed between thespherical mirror and the imager. A mirror such as this has a concavereflecting surface and a layer of refracting material. The light raysthat come from the imager and are directed towards the spherical mirrorpass first of all through the refracting material and are then reflectedon the reflecting surface before passing through the refracting materialfor a second time. A Mangin type mirror has a different optical power onthe one hand in the plane of incidence of the optical axis and, on theother hand, in a perpendicular plane.

According to the invention, this mirror is inclined with respect to theoptical axis.

The thickness of the refracting material may vary on the surface of themirror.

The characteristics of thickness and of optical index of the refractingmaterial enable compensation for the deterioration of resolutionintroduced by the reflecting surface correcting the off-centringdistortion of the second kind.

Various surfaces may be used to make a mirror according to theinvention. The choice of the surfaces depends on the distortion to becompensated for.

The Mangin type mirror may comprise an aspherical reflecting surface anda spherical refracting surface. The aspherical surface is preferably asimple surface of revolution. It may be a torus or it may be a surfacegenerated by a parabola or an ellipse.

The Mangin type mirror may conversely comprise a spherical reflectingsurface and an aspherical refracting surface. The image observed is inthis case less sensitive to the constructional imperfections of themirror.

A mirror according to the invention may even have two asphericalsurfaces. It is then more costly but makes it possible to obtain acorrection that is better overall.

A mirror according to the invention may also have a refracting materialwhose index varies with the position on the mirror surface.

The image of pupil of the eye by the spherical off-axis mirror is thefirst pupil image of the device. It is inclined with respect to theoptical axis. From this first inclined pupil image, the Mangin typemirror according to the invention gives a second pupil image that isrectified on the optical axis.

The device also has a power unit placed between the spherical mirror andthe Mangin type mirror.

The invention makes it possible to preserve an image of high resolutionwhile at the same time providing for thorough correction of thedistortion due to the inclined collimation mirror. The invention has theadvantage of correcting the distortion of the image presented to theuser's eye for a wide instrument pupil, for example with a diameter ofat least 15 millimeters, and for a wide field that is typically greaterthan 40 degrees. The instrument pupil is the zone of space in which theuser of an instrument must place the pupil of his/her eye in order touse it.

Whereas the invention is presented in a plane, it is always possible,after the theoretical positioning of the various optical elements of theinvention, to add one or more plane mirrors that introduce no aberrationbut can be used to meet space requirement constraints for example sothat the device may be adapted to the contour of the user's head.

The invention can be integrated into a helmet viewfinder having a wideinstrument pupil and a wide field.

BRIEF DESCRIPTION OF THE DRAWING

Other features and advantages of the invention shall appear from readingthe following detailed description of particular embodiments made withreference to the following appended drawings in which the opticaldiagrams are shown in a plane known as the plane of symmetry of theoptic.

FIG. 1 shows schematically and partially an optical device with anoff-optical axis spherical combiner mirror.

FIG. 2 shows a device according to the invention whose Mangin typemirror has a reflecting torus and a refracting sphere;

FIG. 3 shows a device according to the invention with another Mangintype mirror where a sphere is reflecting and a torus is refracting.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

In FIG. 1, a user of an optical device comprising a spherical mirror 1is represented by the plane of the pupils 2 and the straight line 5normal to this plane 2. The pupil 11 of the eye is generally located,optically, three millimeters behind the cornea 12 of the eye 3.

It is noted that, depending on its orientation with respect to theuser's face, the straight line 5 may correspond to the user's viewstraight ahead or else to an upward or downward view, a view towards oneside or the opposite side.

The spherical mirror 1 is placed in front of the user. Its concavity isturned towards the user, and the surface of this mirror is in thevicinity of its point of intersection 6 with the straight line 5.

The spherical mirror 1 is supported by a sphere S whose centre 4 doesnot belong to this straight line 5. The plane P of FIG. 1 is a plane ofthe space that contains the centre of the supporting sphere of thespherical mirror 1 and the straight line 5 passing through the centre ofthe pupil 11 of the eye 3. It is the plane of incidence of the straightline 5 on the spherical mirror 1, and it is called the plane of symmetryof the optic. Most usually, this plane is the same as the plane passingthrough the centre of the pupil 11 and is parallel to the theoreticalplane of symmetry of the user's face.

The straight line 5 and the radius 7 of the sphere S passing through thepoint of intersection 6 deviate from each other by an angle θ. Anon-zero value of this angle θ characterizes an off-axis use of thespherical mirror 1. The spherical mirror 1 itself is said to be“off-axis”, and it is inclined.

Consider an optical ray 8 which is symmetrical with the straight line 5of the optical axis with respect to the radius 7 of the sphere S. As afirst approximation, an image whose centre 9 is placed at a distanceequal to half of the radius of curvature of the sphere S on this opticalray is perceived by the user's eye 3 as collimated to first order sincethe light rays coming from the image thus placed are reflected by thespherical mirror 1 towards the eye 3 in the form of a beam ofsubstantially parallel rays. The image with centre 9 may have fieldcurvature.

However, the collimation by reflection on the spherical mirror is notperfect. It is affected not only by aberrations intrinsic to this mirrorbut also by an off-centring optical aberration due to the off-axis useof the spherical mirror 1.

Various optical elements will be described so that the user's eye can bemade to perceive a high-quality collimated image, from a light imageprovided by an imager and collimated by an inclined non-plane mirror. Asimple example of an inclined non-plane mirror effecting collimation isan inclined spherical mirror.

The spherical mirror 1 may be semi-transparent. In this case, light rays10 coming from the environment external to the spherical mirror 1,namely striking the convex face of this mirror, are transmitted to theeye 3 by the spherical mirror 1. This spherical mirror 1 then affords acombiner which superimposes a collimated image on the direct view of theenvironment.

The central field is defined as the beam of light rays coming from thecentre 9 of the image to be collimated. A particular light ray isconsidered which belongs to the central field and passes through thecentre of the user's pupil. The path of this light ray is the opticalaxis of the device used. The optical axis is generally a jagged line.The straight line 5 supports part of the optical axis. Most usually, theimage is presented straight ahead of the user. The straight line 5 isthen substantially normal to the user's face but the image may be forexample presented at the top of the user's resting field of vision atinfinity and the straight line 5 is then oriented in the correspondingdirection.

In FIG. 2, paths of light rays within an embodiment of a deviceaccording to the invention are shown.

In this embodiment, the imager, which is not shown, comprises a screen,for example the screen of a cathode-ray tube or a liquid crystal screen.The screen may also be formed, for example, by a section of a bundle ofoptical fibres or a slide or the screen of a light intensifier tube. Animage having any surface is displayed on the screen of the imagerrepresented by its tangent plane 20. The image may be spherical. It mayequally well be plane. The path of the light rays from the screen of theimager up to the user's eye 3 are plotted for this embodiment of theinvention.

The device comprises an off-axis spherical mirror 1. The devicefurthermore comprises a Mangin type concave mirror 21.

The light rays coming from the screen 20 of the imager strike the Mangintype mirror 21. A mirror such as this has a concave reflecting surface23 and a layer of refracting material 27. The light rays coming from theimager pass first of all through the refracting material and are thenreflected on the reflecting surface before passing through therefracting material a second time.

The light rays reflected by the Mangin type mirror 21 pass through apower unit 22 before striking the off-axis spherical mirror 1 whichprovides for a collimation of the image received by the user's eye 3.

It is now possible to observe the path of the light rays in the otherdirection, namely starting from the user's eye 3 and backtrackingthrough the different optical elements towards the screen of the displayunit.

The rays coming from the eye are reflected on the off-axis sphericalmirror 1. The optical axis which, in the example of FIG. 2, ishorizontal on a first part 31 between the centre of the pupil of the eye3 and the spherical mirror 1 is also reflected on the spherical mirror1.

This part 31 of the optical axis and its reflection on the sphericalmirror 1 define a plane known as the plane of incidence P of the opticalaxis on the off-axis spherical mirror 1.

In the example of FIG. 2, the plane of incidence is the same as theplane P of symmetry of the optic which is represented by the plane ofFIG. 2. The plane of symmetry of the optic is a plane containing thepath described by the optical axis between the imager and the user'spupil. However, an embodiment of the invention is not limited to anoptic in this plane P; in the context of the invention, it is alwayspossible to add additional plane mirrors making it possible to takeoptical elements outside the plane P. Indeed, the plane mirrors, whichare also called folding mirrors, do not modify the optical function,they do not introduce and do not correct any aberration but they enablethe optical rays to circumvent obstacles such as the user's head.

The reflected rays strike, in this exemplary embodiment, a plane mirror50 that enables the folding of the optical rays while preserving theplane of incidence of the optical axis on the spherical mirror 1. Theinvention may be embodied without this plane mirror 50. After reflectionon the plane mirror 50, the optical axis is oriented along a straightline 32 of the plane of incidence.

On this second part 32 of the optical axis may be observed a first pupilimage 24 that is the image of the pupil of the eye 3 given by theoff-axis spherical mirror 1.

The normal 25 to the plane tangential to this first pupil image 24 isnot parallel to the corresponding section 32 of the optical axis. Thefirst pupil image 24 is inclined on the optical axis.

A power unit 22 is placed for example so that the first pupil image 24is in the path of the light rays between the spherical mirror 1 and thepower unit 22.

The first pupil image 24 is on one side of the power unit 22 and theMangin type mirror 21 is on the other side. The Mangin type concavemirror 21 is in the path of the rays that come from the pupil of the eye3—since the description as given herein backtracks along the real pathof the light rays coming from the screen of the imager—and to reflect[sic ] these rays towards the screen 20 of the imager. The plane P ofFIG. 2 is also the plane of incidence of the optical axis on the Mangintype mirror 21.

On emerging from the mirror 21 and heading towards the screen of theimager 20, the optical axis is aligned with a straight line 33 thatrepresents a third part of the optical axis.

The useful part of the Mangin type mirror 21 has a tangent plane Q whosenormal 28, belonging to the plane of incidence P, is not parallel to thethird part 33 of the optical axis. The Mangin type mirror 21 is inclinedwith respect to the optical axis. It is said to be off-axis.

A Mangin mirror is a meniscus having a reflecting surface and arefracting surface.

In this first embodiment of the invention, the Mangin type mirror has asimple structure close to that of a Mangin mirror. Its refractingsurface, supported by a sphere, can easily be made of optical glass witha constant index. Its reflecting surface is an aspherical surface havinga symmetry of revolution in order to facilitate the making of the Mangintype optical element and limit the cost of its manufacture.

This surface is for example the surface generated by the rotationalmotion of an arc of a circle belonging to the plane P around an axis ofrevolution also belonging to the plane P. Thus, in the plane ofincidence P containing the two parts 31, 32 of the optical axis thathave been described, the Mangin type mirror 21 has a constant radius ofcurvature.

Consider a plane R perpendicular to the plane of incidence P and to thetangent plane Q. The plane R is perpendicular to the axis of revolution.In this first embodiment, the curvature of the reflecting face on theMangin type mirror 21 is also constant in the plane R but it isdifferent from the curvature in the plane P. This mirror 21 is aspherical-toroidal lens whose aspherical surface is treated so as to bereflecting.

The curvatures defining the spherical-toroidal lens enable finecorrection of the distortion due to the spherical mirror 1 while at thesame time preserving a high degree of sharpness of the collimated image.

The curvatures of the reflecting surface are used to rectify the imagein order to correct the distortion.

The thickness of the Mangin type mirror is used to compensate for theastigmatism introduced by the thorough correction of the distortion bymeans of the reflecting aspherical surface.

In variant embodiments, the aspherical surface of this mirror 21 has aradius of curvature that is variable in the plane of incidence P. Thesevariants, which are more difficult to make, enable correction of thedistortion with a finer resolution (or a better correction of thedistortion for one and the same resolution).

In one of these variants, the intersection of the aspherical surfacewith the plane P is a parabola. The surface may even by supported by aparaboloid of revolution.

In another variant embodiment, the intersection of the asphericalsurface with the plane P is a non-degenerate ellipse (namely an ellipsewhose radius of curvature is not constant).

In another variant, the aspherical surface describes a part of anellipsoid, which may have a symmetry of revolution.

In the first embodiment of the invention shown in FIG. 2, constraints ofspace requirement on the entire optic lead, firstly, to the minimizingof the envelope of the beam of optical rays and, secondly, to thedesigning of spaces for adding folding mirrors. The entire optic maythen for example match the shape of the user's skull.

The optical power of the mirror 21, chosen for this embodiment, makes itpossible to limit the volume of the beam of rays coming from the imager20 in the vicinity of the Mangin type mirror.

And the power unit 22 tends to restrict the surface area of the Mangintype mirror 21.

It is noted that when there are no constraints of space requirement, ahighly efficient device in terms of resolution and correction ofdistortion would have a useful surface area of the mirror 21 that isgreater by about 50% and a magnification factor of the pupillaryconjugation of the mirror 21 that is nearly twice unity.

In the embodiment of FIG. 2, the magnification factor of the pupillaryimages conjugated by the Mangin type mirror is kept close to unity.

The embodiment of FIG. 2 furthermore comprises a relaying optic 29 tomeet the constraints of space requirement of the optic and of the imagerand to adapt the magnification of the image displayed on the screen 20for its presentation to the user.

The relaying optic 29 is placed between the screen of the imager 20 andthe Mangin type mirror 21. A sufficient run is left between the Mangintype mirror 21 and the first lens of the unit 29 to fold the system bymeans of a plane mirror.

The relaying optic 29 is substantially aligned with the third part 33 ofthe optical axis.

In this third part 33 of the optical axis, a second pupillary image 30can be seen, located between the Mangin type mirror 21 and the imager20.

The pupillary image 30 has a tangent plane that is substantially normalto the optical axis 33: this is a correction introduced by theaspherical mirror 21. Indeed, the first image 24 of the pupil of the eyeformed by the spherical mirror 1 is inclined with respect to the localoptical axis 32 and corresponds to the aberrations induced by thismirror 1. The second pupillary image 30 is rectified with respect to theoptical axis 33 by the aspherical mirror 21. It is substantiallyperpendicular to the optical axis 33.

In FIG. 2, an optical cube 26 is placed in the relaying optic 29 toenable the mixing of the image of the screen of the imager 20 with animage of a second imager (not shown). This cube 26 makes it possible forexample to superimpose an image of symbols coming from the screen 20 andan image of the night landscape coming from the screen of a lightintensifier.

The first described embodiment of the invention is illustrated by FIG.2, the Mangin type mirror 21 has a spherical refracting surface and anaspherical reflecting surface.

However, for reasons of practical embodiment, a second embodiment shownin FIG. 3 will be preferred. In this second embodiment, the Mangin typemirror 41, which is inclined on the local optical axis, has anaspherical refracting surface and a spherical reflecting surface.

Indeed, the aspherical surface is more difficult to make than thespherical surface and the imperfections of the refracting surface leadto fewer penalties than the imperfections of the reflecting surface forthe Mangin type mirror.

More specifically, the refracting surface of the mirror 41 of FIG. 3 isa torus.

Alternatives of this second embodiment comprise an aspherical surfacethat is distinct from the torus such as for example the asphericalsurfaces described in the first embodiment of the invention.

To enable a more thorough correction of the distortion with highresolution, a third embodiment comprises a Mangin type mirror whose twosurfaces are aspherical.

The choice of the two surfaces enables an efficient correction of thedistortion associated with high resolution (or high sharpness) of theimage.

The quality of the image presented to the user, which is evaluated viaits resolution and its residual distortion, is then improved at the costof the construction of more complex surfaces for the Mangin type mirror.

A third embodiment (not shown) of the invention comprises a Mangin typemirror whose refracting material has an optical index that is variableaccording to the position on the surface of the mirror.

The off-axis spherical mirror 1 may be semi-transparent. In this case,the light rays emitted by the landscape or the environment in the fieldof view of the user are transmitted by this mirror and are received bythe pupil of the eye simultaneously with the rays that are reflected bythis same mirror and have been described hereinabove. Thesemi-transparent mirror is a combiner. It is therefore a sphericalcombiner used off-axis.

The combiner preferably forms part of a visor for the protection of theeyes and even the face of the user.

A visor according to the invention has at least one off-axis reflectingpart. In the position of use, the visor is lowered so that the partcorresponding to the collimation mirror is placed in front of the user'seye. The entire device for presenting collimated images 20, 21, 22, 1may be integrated into a helmet for example, for an aircraft orhelicopter pilot, and enables the making of a helmet viewfinder.

The viewfinder may be monocular if it presents the collimated image toone eye only.

The viewfinder may be binocular if it presents an image for each eye. Ithas the advantage of providing for pleasant vision when the overlappingof the fields of view of the two images is total.

A binocular viewfinder may also present a partial overlapping of the twofields of view. This makes it possible, for one and the samedimensioning of the optics, to obtain a wider field of view withoutcausing excessive deterioration in the perception of the informationpresented.

The distortion of an image having a grid leads to the deformation of thegrid. The images presented to the user, in which the distortion inherentto the off-axis concave visor is corrected, are particularlyadvantageous for a helmet viewfinder for they conform to the actualdimensions of the objects represented. This is paramount when theviewfinder presents an image superimposed on the direct view and is evenmore so when the image presented replaces the direct view for the user,for example in the case of night vision assisted by an imageintensifier, of infrared vision or of a training simulator.

What is claimed is:
 1. Optical device for a system for a presentation ofcollimated images through the pupil of the eye of a user, comprising: animager with an optical axis defined by a path of a ray passing through acentre of the pupil of the eye and a centre of the imager; an off-axisconcave mirror inclined with respect to a first part of the optical axisdefined by a line between the centre of the pupil and a centre of theoff-axis concave mirror; and a Mangin mirror inclined on a second partof the optical axis corresponding to a reflection of the first part ofthe optical axis on the concave mirror, wherein the Mangin mirrorincludes a refracting material configured to correct an off-axisdistortion of the image presented to the user due to the off-axisconcave mirror.
 2. Device according to claim 1, wherein the Manginmirror comprises: a first reflecting surface; and a layer of therefracting material defining a second reflecting surface, wherein thethickness of the layer between the two surfaces is not constant. 3.Device according to claim 2, wherein the refracting and reflectingsurfaces of the Mangin mirror are aspherical.
 4. Device according toclaim 2, wherein the Mangin mirror has a spherical refracting surfaceand an aspherical reflecting surface.
 5. Device according to claim 2,wherein the Mangin mirror has an aspherical refracting surface and aspherical reflecting surface.
 6. Device according to claim 3, wherein atleast one aspherical surface of the Mangin mirror is a torus.
 7. Deviceaccording to claim 3, wherein the Mangin mirror has two curves ofintersection with a plane of incidence of the optical axis and at leastone of the curves has a variable curvature.
 8. Device according to claim7, wherein the curve having a variable curvature is at least one of aparabola and an ellipse.
 9. Device according to claim 3, wherein atleast one aspherical surface of the Mangin mirror is supported by aparaboloid.
 10. Device according to claim 3, wherein at least oneaspherical surface of the Mangin mirror is supported by an ellipsoid.11. Device according to claim 1, wherein the refracting material has anoptical index that is variable with a position on a surface of theMangin mirror.
 12. Device according to claim 1, wherein the devicecomprises: a power unit placed between the concave mirror and the Manginmirror.
 13. Device according to claim 1, wherein the concave mirror isspherical and inclined with respect to a direction of observation. 14.Device according to claim 1, wherein the concave mirror issemi-transparent.
 15. Device according to claim 1, wherein the systemfor the presentation of collimated images is a helmet viewfinder.